Answer:
The Immune system is a complex network of cells (such as lymphocytes) and organs that work together to defend the body against foreign substances (antigens) such as bacteria, a virus or tumor cell.
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a positron emission tomography (PET) scan is an imaging test that allows your doctor to check for diseases in your body. The scan uses a special dye containing radioactive tracers. These tracers are either swallowed, inhaled, or injected into a vein in your arm depending on what part of the body is being examined
